The present invention relates generally to projection lithographic methods and systems for producing integrated circuits and forming patterns with extremely small feature dimensions. The present invention relates particularly to extreme ultraviolet soft x-ray based lithography and reflective masks which reflect extreme ultraviolet soft x-ray radiation and form pattern images that are utilized to form circuit patterns. The present invention relates to reflective masks and their use for reflecting extreme ultraviolet soft x-ray photons to enable the use of extreme ultraviolet soft x-ray radiation for lithography that surpasses current optical lithography circuit feature dimension performance.
The use of extreme ultraviolet soft x-ray radiation provides benefits in terms of achieving smaller feature dimensions but due to the nature of the radiation, it presents difficulties in terms of manipulating and directing such wavelengths of radiation and has delayed the commercial manufacturing use of such radiation. Current optical lithography systems used in the manufacturing of integrated circuits have progressed towards shorter optical wavelengths of light, such as from 248 nm to 193 nm to 157 nm, but the commercial use and adoption of extreme ultraviolet soft x-rays has been hindered. Part of this slow progression to very short wavelengths of radiation such as in the 15 nm range, has been due to the lack of economically manufacturable reflective mask wafers that can withstand the exposure to such radiation while maintaining a stable and high quality circuit pattern image. For the benefits of extreme ultraviolet soft x-rays to be utilized in the manufacturing of integrated circuits, there is a need for a stable glass wafer that allows for direct deposition of reflective coatings to the surface of the glass wafer.
As noted from U.S. Pat. No. 5,698,113, current extreme ultraviolet soft x-ray lithographic systems are extremely expensive. U.S. Pat. No. 5,698,113 tries to address such high costs by trying to recover the surfaces of multilayer coated substrates by etching the multilayer reflective coatings from substrate surfaces of fused silica and ZERODUR type aluminosilicate glass-ceramics, even though such etching degrades the substrate surface.
The present invention provides for an economically manufactured mask wafer that is stable, ready for direct coating and receptive to receiving multilayer reflective coatings and provides an improved extreme ultraviolet soft x-ray based projection lithography method/system. The present invention economically provides for improved mask wafer performance and stability without the need to recycle the mask wafer surface which has been shown to reduce performance and the reflectivity of the mask. The present invention provides a stable high performance reflective mask with the reflective multilayer coating directly deposited on the finished glass surface, and avoids costly and cumbersome manufacturing steps and intermediate layers between the glass substrate surface and the reflective multilayer coating.
One aspect of the present invention is a projection lithographic method/system for producing integrated circuits with printed feature dimensions less than 100 nm that includes providing an illumination sub-system for producing and directing an extreme ultraviolet soft x-ray radiation xcex from an extreme ultraviolet soft x-ray source. The method further includes providing a mask sub-system illuminated by the extreme ultraviolet soft x-ray radiation xcex produced by the illumination sub-system and providing the mask sub-system includes providing a patterned reflective mask for forming a projected mask pattern when illuminated by radiation xcex. Providing the patterned reflective mask includes providing a Ti doped high purity SiO2 glass wafer with a patterned absorbing overlay overlaying the reflective multilayer coated Ti doped high purity SiO2 glass defect free wafer surface that has an Ra roughnessxe2x89xa60.15 nm. The method further includes providing a projection sub-system and an integrated circuit wafer which has a radiation sensitive wafer surface wherein the projection sub-system projects the projected mask pattern from the patterned reflective mask onto the radiation sensitive wafer surface.
In another aspect, the present invention includes a method of making a projection lithographic system and a method of projection lithography that includes providing an illumination sub-system which has an extreme ultraviolet soft x-ray source and providing a mask sub-system that has a mask receiving member and a reflective mask Ti doped high purity SiO2 glass mask wafer with an unetched glass mask surface coated with a reflective multilayer coating having a reflectivity of at least 65% to extreme ultraviolet soft x-rays that is received in the mask receiving member. The method further includes providing a projection sub-system including a camera with a depth of focus xe2x89xa71 xcexcm and a numerical aperture NAxe2x89xa60.1; providing a radiation sensitive print sub-system with a radiation sensitive print media; and aligning the illumination sub-system, the mask sub-system, the projection sub-system, and the radiation sensitive print sub-system wherein the extreme ultraviolet soft x-ray source illuminates the reflective mask with extreme ultraviolet soft x-ray radiation and forms a printing pattern which is projected by the projection sub-system camera onto said radiation sensitive print media.
The invention further includes a method of making a reflective extreme ultraviolet soft x-ray mask which includes the steps of: providing a Ti doped high purity SiO2 glass preform having a preform surface and free of inclusions, finishing the preform surface into a planar mask wafer surface with an Ra surface roughnessxe2x89xa60.15 nm, and coating the finished planar mask wafer surface with a reflective multilayer coating to form a reflective mask surface having a reflectivity of at least 65% to extreme ultraviolet soft x-rays.
The invention also includes a reflective extreme ultraviolet soft x-ray mask wafer that comprises a Ti doped high purity SiO2 inclusion-free glass wafer having an unetched first polished planar face surface and an opposing second polished planar face surface, with the first surface free of printable surface defects that have a dimension greater than 80 nm and has a Ra roughnessxe2x89xa60.15 nm.
The invention further includes a method of making a reflective extreme ultraviolet soft x-ray mask wafer that has the steps of: providing a Ti doped high purity SiO2 glass preform with a first preform surface and an opposing second preform surface, and is free of inclusions, and finishing the first preform surface into a planar mask wafer surface having an Ra roughnessxe2x89xa60.15 nm.
Additional features and advantage of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended Figures.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying Figures are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The Figures illustrate various embodiments of the invention, and together with the description serve to explain the principals and operation of the invention.